Combo Box

Change parameter or variable value during simulation using combo box with customizable appearance

Since R2025a

• 

Libraries:
Simulink / Dashboard / Customizable Blocks

Description

Use the Combo Box block to change the value of the connected parameter or variable before or during simulation. When you use the Combo Box block in the Customizable Blocks library, you can customize the appearance of the block, for example, to make the block look like a combo box in a digital user interface you are designing. Use the Combo Box block with other dashboard blocks to build an interactive dashboard of controls and indicators for your model.

Each option in the combo box drop-down list corresponds to a state of the Combo Box block. The state has a label and a value. The state label is the text in the drop-down list that identifies the option. When you select an option, the Combo Box block enters the associated state and assigns the state value to the connected parameter. To select an option during simulation, click the Combo Box block to expand the drop-down list, and then select the option. To select an option when the simulation is not running, click the Combo Box block to select the block, click the block again to expand the drop-down list, and then select the option.

To customize the state label or value, open the Parameters tab of the Property Inspector or the Block Parameters dialog box.

Note

• Double-clicking a connected Combo Box block during simulation or after clicking the block does not open the Block Parameters dialog box. To open the Block Parameters dialog box, press Shift, then double-click the block.

• Clicking a connected Combo Box block during simulation both selects the block and expands the combo box drop-down list. To select the block without expanding the list, press Shift, then click the block.

Customize Combo Box Blocks

When you add a Combo Box block to your model, the block is preconfigured with a default design. You can use the block with the default design or customize the appearance of the block.

To customize the appearance of the block, use design mode. After selecting the block, you can enter design mode in one of three ways:

• In the Simulink^® Toolstrip, on the block-specific tab, under Design, click Edit.

• In the Property Inspector, on the Design tab, click Edit.

• Pause on the ellipsis that appears over the block and click the Edit Custom Block button .

In design mode, you can use the toolbar above the block to customize the combo box. To access additional customization options or to enter exact values for design settings, use the Design tab in the Property Inspector.

Design Mode Actions

Action	Available in Toolbar	Available in Design Tab
Change the value each option assigns to the connected parameter.	No	Yes
Change the text of the option labels.	No	Yes
Add or remove options.	Yes	Yes
Change the chevron icon of the drop-down list.	No	Yes
Change the number of visible entries in the drop-down list.	No	Yes
Change the background and border color of the drop-down list.	No	Yes
Change the background, border, and font color of the highlighted entry in the drop-down list.	No	Yes
Upload a background image.	No	Yes
Set a solid background color.	No	Yes
Upload a foreground image.	No	Yes

When you finish editing the design, to exit design mode, click the X in the upper right of the canvas.

Connect Dashboard Blocks

Dashboard blocks do not use ports to connect to model elements. To connect a dashboard block, use connect mode. To enter connect mode on an unconnected block, pause on the block you want to connect and click the Connect button . To enter connect mode on a connected block, select the block, pause on the ellipsis that appears (…), and in the action menu that expands, click the Connect button.

To connect a control block to a parameter in your model or to change the connection of a control block, enter connect mode. Select the block to whose parameter you want to connect. From the list that appears, select the parameter to which you want to connect. Then, pause on the dashboard block and click the Done Connecting button .

The control block cannot connect to a parameter defined by a variable until you update the model diagram. To connect to a parameter defined by a variable or to modify the value of a variable that defines the value of a connected parameter when the simulation is not running, update the model diagram by pressing Ctrl+D.

You can connect to a parameter with a scalar value or to an element of a matrix or structure. For more information, see Connect Dashboard Blocks to Simulink Model.

You can also connect dashboard blocks to a Stateflow^® chart. For more information, see Connect Dashboard Blocks to Stateflow (Stateflow).

This animation shows how to connect the Combo Box block to your model.

Parameter Logging

Tunable parameters connected to dashboard blocks are logged to the Simulation Data Inspector, where you can view the parameter values along with logged signal data. You can access logged parameter data in the MATLAB^® workspace by exporting the parameter data from the Simulation Data Inspector by using the UI or the Simulink.sdi.exportRun function. For more information about exporting data using the Simulation Data Inspector UI, see Export Data to Workspace or File. The parameter data is stored in a Simulink.SimulationData.Parameter object, accessible as an element in the exported Simulink.SimulationData.Dataset.

Limitations

• Except for the Dashboard Scope block and the Display block, dashboard blocks can only connect to real scalar signals.

• You cannot use the Connection table in the Block Parameters dialog box to connect a dashboard block to a block that is commented out. When you connect a dashboard block to a commented block using connect mode, the dashboard block does not display the connected value until the you uncomment the block.

• Dashboard blocks cannot connect to model elements inside referenced models.

• When you simulate a model hierarchy, dashboard blocks inside referenced models do not update.

• Dashboard blocks do not support rapid accelerator simulation.

• When you connect a dashboard block to a variable or parameter during simulation, the data for that variable or parameter is not logged to the Simulation Data Inspector. To log variable and parameter data to the Simulation Data Inspector, connect the dashboard block to the variable or parameter prior to simulation.

• When you simulate a model in external mode with the Default parameter behavior set to Inlined, dashboard blocks can appear to change parameter and variable values. However, the change does not propagate to the simulation. For example, Gain blocks display changes made to the Gain parameter using the dashboard blocks, but the Gain value used in the simulation does not change.

Parameters

Use the Property Inspector and the Block Parameters dialog box to specify the values of the block parameters. To set the core parameters of the dashboard block, use the Block Parameters dialog box or the Parameters tab in the Property Inspector. To customize the block, use the Design tab in the Property Inspector. To open the Block Parameters dialog box for a block, double-click the block. To open the Property Inspector, on the Modeling tab, under Design, select Property Inspector.

Parameters

To set the core parameters of the dashboard block, open the Property Inspector and click the Parameters tab.

Connection

Connection — Block parameter value to connect

parameter value connection options

Dashboard blocks do not use ports to connect to model elements. To connect dashboard blocks to parameter values in your model, use connect mode, the Simulink Toolstrip, or the Connection table in the Block Parameters dialog box. To open the Block Parameters dialog box from the Property Inspector, to the right of Connected to, click Connect or Change. You can connect to a parameter with a scalar value, or to an element of a matrix. For information about connect mode and how to connect using the toolstrip, see Connect Dashboard Blocks to Simulink Model.

To connect a control block to a parameter with a scalar value or change the connection of a control block to a parameter with a scalar value using the Connection table:

1. Select the block.

2. To connect the block, in the Property Inspector, on the Parameters tab, click Connect. To change the connection of the block, click Change instead.

3. Select the block to whose parameter value you want to connect.

4. In the table, select the parameter to which you want to connect.

5. Click Apply.

The control block cannot connect to a parameter defined by a variable until you update the model diagram. To connect to a parameter defined by a variable or to modify the value of a variable that defines the value of a connected parameter when the simulation is not running, update the model diagram by pressing Ctrl+D.

You can also connect dashboard blocks to a Stateflow chart. For more information, see Connect Dashboard Blocks to Stateflow (Stateflow).

Programmatic Use

To programmatically connect a dashboard block to a tunable parameter, use a Simulink.HMI.ParamSourceInfo object. The Simulink.HMI.ParamSourceInfo object contains four properties. Some properties apply to connecting dashboard blocks to parameters defined by values, and some apply to connecting dashboard blocks to parameters defined by variables. Not all fields have a value for a connection because a given dashboard block connects to either to a parameter defined by a value or to a parameter defined by a variable.

Block Parameter: Binding

Type: Simulink.HMI.ParamSourceInfo

Default: []

Main

Label — Position of label displaying name of connected element

Hide (default) | Bottom | Top

You can display the name of the element to which the dashboard block connects in a label positioned at the top or bottom of the block, or you can hide the label. If you want the label to be visible, specify the position of the label. If you do not want the label to be visible, select Hide.

Note

When the dashboard block is not connected to an element, the label is blank.

Programmatic Use

Block Parameter: LabelPosition

Type: character vector

Values: 'Hide' | 'Bottom' | 'Top'

Default: 'Hide'

Lock Aspect Ratio — Option to maintain block aspect ratio

on (default) | off

Select this parameter to maintain the aspect ratio when resizing the block in the Simulink canvas.

When the aspect ratio is locked, adding a new background image changes the aspect ratio of the block to match the aspect ratio of the background image. When the aspect ratio is unlocked, adding a new background image does not change the aspect ratio of the block, but instead changes the aspect ratio of the background image to fit the size of the block.

When the aspect ratio is locked, pressing the Shift key while resizing a block temporarily unlocks the aspect ratio. When you release the Shift key, the aspect ratio locks. When the aspect ratio is unlocked, pressing the Shift key while resizing a block temporarily locks the aspect ratio. When you release the Shift key, the aspect ratio unlocks.

Enumerated Data Type — Option to specify state values and labels using enumerated data type

off (default) | on

To configure the state labels and values for the block, you can use an enumerated data type that pairs each enumeration with a numeric value. First, select Enumerated Data Type. Then, specify the name of the enumerated data type in the text box. The definition for the specified enumerated data type must be saved on the MATLAB path or in the base workspace.

Note

You can define an enumerated data type using the Simulink.defineIntEnumType function. For example, to define the enumerated data type myEnumType for a set of Roman numerals from one to five, use this command.

Simulink.defineIntEnumType('myEnumType',...
    {'I','II','III','IV','V'}, [1 2 3 4 5]);

Then, in the Property Inspector, on the Parameters tab, in the Enumerated Data Type text box, enter myEnumType.

States — Management and configuration of states

scalar and character vector

Each option in the combo box drop-down list corresponds to a state of the Combo Box block. The state has a label and a value. The State Label value is the text in the drop-down list that identifies the option. When you select an option, the Combo Box block enters the associated state and assigns the State Value value to the connected parameter.

By default, the block has three combo box options and three corresponding states.

State Value	State Label
0	Label1
1	Label2
2	Label3

You can design a Combo Box block with any number of states greater than or equal to 1. To add a new state, click the + button. To delete a state, click the label text in the State Label column or the value in the State Value column, and then click the - button.

Note

When Enumerated Data Type is turned on, you cannot add or delete states. You can turn off this option in the Parameters tab of the Property Inspector.

To configure the label text or value of a state, click the label text in the State Label column or the value in the State Value column, delete the current value, enter a new value, and press Enter.

Tip

You can also configure the parameters for a state in design mode:

1. Select the Combo Box block.

2. Enter design mode. In the Property Inspector, on the Design tab, click Edit.

3. On the Design tab, open the States component, expand the Select State section, and from the drop-down menu, select the state that you want to configure.

4. Configure the label text and value of the selected state in the Text and Value text boxes.

Design

To customize the dashboard block, open the Property Inspector, click the Design tab, and click Edit. Changes you make to the values of the parameters in this section are applied to all combo box options.

Combo Box

Lock Aspect Ratio — Option to maintain block aspect ratio

on (default) | off

Select this parameter to maintain the aspect ratio when resizing the block in the Simulink canvas.

When the aspect ratio is locked, adding a new background image changes the aspect ratio of the block to match that of the background image. When the aspect ratio is unlocked, adding a new background image does not change the proportions of the block but instead stretches or scales the background image to fit the size of the block.

When the aspect ratio is locked, pressing the Shift key while resizing a block unlocks the aspect ratio. When you release the Shift key, the aspect ratio locks. When the aspect ratio is unlocked, pressing the Shift key while resizing a block locks the aspect ratio. When you release the Shift key, the aspect ratio unlocks.

Dropdown Background Color — Background color of drop-down list

[r g b] vector

Choose a background color for the drop-down list from the palette of standard colors, or specify a custom color.

Dropdown Border Color — Color of border around drop-down list

[r g b] vector

Choose a color for the border around the drop-down list from the palette of standard colors, or specify a custom color.

Visible Entries — Maximum number of options visible in drop-down list

scalar

By default, when you expand the drop-down list a maximum of five combo box options are visible. You can access any options that are not visible by scrolling. Specify the maximum number of options that are visible when you expand the drop-down list.

Highlight Background Color — Background color of highlighted option in drop-down list

[r g b] vector

Choose a background color for the highlighted option in the drop-down list from the palette of standard colors, or specify a custom color.

Highlight Border Color — Color of border around highlighted option in drop-down list

[r g b] vector

Choose a color for the border around the highlighted option in the drop-down list from the palette of standard colors, or specify a custom color.

Highlight Font Color — Font color of highlighted option in drop-down list

[r g b] vector

Choose a font color for the highlighted option in the drop-down list from the palette of standard colors, or specify a custom color.

Width — Chevron width

scalar

Specify the width of the chevron as a ratio of the font height of the label text.

Example: 0.5

Height — Chevron height

scalar

Specify the height of the chevron as a ratio of the font height of the label text.

Example: 0.5

Lock Aspect Ratio — Option to maintain chevron aspect ratio

on (default) | off

Turn on this option to maintain the aspect ratio when resizing the chevron using the Property Inspector.

States

Select State — State label and value

scalar and character vector

Each option in the combo box drop-down list corresponds to a state of the Combo Box block. The state has a label and a value. The State Label value is the text in the drop-down list that identifies the option. When you select an option, the Combo Box block enters the associated state and assigns the State Value value to the connected parameter.

By default, the block has three combo box options and three corresponding states.

State Value	State Label
0	Label1
1	Label2
2	Label3

You can design a Combo Box block with any number of states greater than or equal to 1. To add a new state, click the + button. To delete a state, in the Select State section, select the state. Then, click the X button.

Note

When Enumerated Data Type is enabled, you cannot add or delete states. You can disable this option in the Parameters tab of the Property Inspector.

To configure the label text or value of a state, in the Select State section, select the state. Then, enter new values in the Value and Text boxes.

Tip

You can also configure the states for the block using the Parameters tab in the Property Inspector.

Value — State value

scalar

Specify the State Value of the state selected in the Select State section.

Note

When Enumerated Data Type is turned on, you cannot change the value. You can turn off this option in the Parameters tab of the Property Inspector.

Text — State label text

string | character array

Specify the State Label text of the state selected in the Select State section.

Note

When Enumerated Data Type is turned on, you cannot change the text. You can turn off this option in the Parameters tab of the Property Inspector.

Background Image

Use Background Color — Option to specify solid block background color

off (default) | on

For the block background, you can provide a background image or select a solid color. To select a solid background color, select this parameter. To provide a background image, clear this parameter.

Note

Changing the background color using the Format tab of the Simulink Toolstrip removes the background image and enables the Use Background Color parameter.

Example: on

Color — Block background color

[r g b] vector

To use a solid background color, select the Use Background Color parameter. Then, choose a background color from the palette of standard colors, or specify a custom color.

Tip

You can also specify the Background Color in the Format tab of the Simulink Toolstrip.

To specify the color of the block text, use the Font Color parameter.

Programmatic Use

Specify the BackgroundColor parameter for the block as a 1-by-3 [r g b] vector with values between 0 and 1 that is formatted as a string or a character vector.

Block Parameter: BackgroundColor

Type: string | character vector

Values: [r g b] vector

Opacity — Block background opacity

1 (default) | scalar

Specify the block background opacity as a scalar value from 0 to 1.

Example: 0.5

Corner Radius — Corner radius of area with block background color

scalar

Specify the corner radius of the area covered by the block background color as a ratio of half of the smaller of the two block dimensions, width or height.

Example: 0.25

Foreground Image

X Offset — Horizontal offset of left edge of foreground image from left edge of block

scalar

Specify the horizontal offset of the left edge of the image from the left edge of the block as a ratio of the block width. Relative to the position of the image when the offset is 0, an offset with a negative value moves the image left, and an offset with a positive value moves the image right.

Example: 1

Y Offset — Vertical offset of top edge of foreground image from top edge of block

scalar

Specify the vertical offset of the top edge of the image from the top edge of the block as a ratio of the block height. Relative to the position of the image when the offset is 0, an offset with a negative value moves the image up, and a positive value moves the image down.

Example: 1

Width — Foreground image width

scalar

Specify the width of the foreground image as a ratio of the block width.

Example: 0.5

Height — Foreground image height

scalar

Specify the height of the foreground image as a ratio of the block height.

Example: 0.5

Lock Aspect Ratio — Option to maintain foreground image aspect ratio

on (default) | off

Select this parameter to maintain the aspect ratio when resizing the image using the Property Inspector.

Block Characteristics

Data Types	double | half | integer | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Dashboard blocks are ignored for code generation.

Version History

Introduced in R2025a

R2025a: Select dashboard block and open Block Parameters dialog box during simulation

When a Simulink block from the Dashboard or Customizable Blocks library is active, you can interact with the gadget the block represents. For example, you can push a button or flip a switch. When a block is inactive, you can only interact with the block. For example, you can move or resize the block. By default, all blocks from the Dashboard and Customizable Blocks libraries are active during simulation. Blocks promoted to a dashboard panel are also active when the panel is open in its own window or docked and unlocked. Callback Button blocks for which at least one of the callbacks triggered by pushing the button has a nonempty value are always active. To interact with the gadget represented by an inactive block, you can temporarily activate a block by clicking the block. When you deselect the block, the block becomes inactive again.

Clicking an active Callback Button block or an active block from the Dashboard or Customizable Blocks library that is connected to a parameter or variable value both selects the block and interacts with the gadget the block represents. For example, clicking an unselected active connected Push Button block both selects the block and pushes the button. Starting in R2025a, you can select the block without interacting with the gadget by pressing Shift and then clicking the block. Similarly, you can open the Block Parameters dialog box by pressing Shift and then double-clicking the block.